Aqueous cleaning processes are a mainstay of both domestic and industrial textile fabric washing. On the assumption that the desired level of cleaning is achieved, the efficacy of such processes is usually characterised by their levels of consumption of energy, water and detergent. In general, the lower the requirements with regard to these three components, the more efficient the washing process is deemed. The downstream effect of reduced water and detergent consumption is also significant, as this minimises the need for disposal of aqueous effluent, which is both extremely costly and detrimental to the environment.
Such washing processes, whether in domestic washing machines or their industrial equivalents (usually referred to as washer extractors), involve aqueous submersion of fabrics followed by soil removal, aqueous soil suspension, and water rinsing. In general, the higher the level of energy (or temperature), water and detergent which is used, the better the cleaning. The key issue, however, concerns water consumption, as this sets the energy requirements (in order to heat the wash water), and the detergent dosage (to achieve the desired detergent concentration). In addition, the water usage level defines the mechanical action of the process on the fabric, which is another important performance parameter; this is the agitation of the cloth surface during washing, which plays a key role in releasing embedded soil. In aqueous processes, such mechanical action is provided by the water usage level, in combination with the drum design, for any particular washing machine. In general terms, it is found that the higher the water level in the drum, the better the mechanical action. Hence, there is a dichotomy created by the desire to improve overall process efficiency (i.e. the reduction of energy, water and detergent consumption), and the need for efficient mechanical action in the wash. For domestic washing in particular there are defined wash performance standards specifically designed to discourage the use of such higher levels in practice, in addition to the obvious cost penalties which are associated with such usage.
Current efficient domestic washing machines have made significant strides towards minimising their consumptions of energy, water and detergent. EU Directive 92/75/CEE sets a standard which defines washing machine energy consumption in kWh/cycle (cotton setting at 60° C.), such that an efficient domestic washing machine will typically consume <0.19 kWh/kg of washload in order to obtain an ‘A’ rating. If water consumption is also considered, then ‘A’ rated machines use <9.7 liters/kg of washload.
Detergent dosage is then driven by manufacturer recommendations but, again, in the domestic market, for a concentrated liquid formulation, a quantity of 35 ml (or 37 g) for a 4-6 kg washload in soft and medium hardness water, increasing to 52 ml (or 55 g) for a 6-8 kg washload (or in hard water or for very dirty items) is typical (see, for example, Unilever pack dosage instructions for Persil® Small & Mighty). Hence, for a 4-6 kg washload in soft/medium water hardness, this equates to a detergent dosage of 7.4-9.2 g/kg whilst, for a 6-8 kg washload (or in hard water or for very dirty items), the range is 6.9-9.2 g/kg.
Energy, water and detergent consumptions in the industrial washing process (washer-extractors) are considerably different, however, and usages of all three resources are less constrained, since these are the principal factors in reducing cycle time—which is, of course, more of a consideration than in the case of domestic use. For a typical industrial washer extractor (25 kg washload rated and above), energy consumption is 0.30-1.0 kWh/kg, water is at 20-30 liters/kg, and detergent is much more heavily dosed than for domestic washing. The exact level of detergent used will depend on the amount of soiling, but a range of 20-100 g/kg is representative.
Thus, it can be taken from the above discussion that it is the performance levels in the domestic sector which set the highest standard for an efficient fabric washing process, and that these are: an energy consumption of <0.19 kWh/kg, a water usage of <9.7 liters/kg, and a detergent dosage of approximately 8.0 g/kg. However, as previously observed, it is becoming increasingly difficult to reduce the water (and, hence, energy and detergent) levels in a purely aqueous process, due to the minimum requirement to wet the fabric thoroughly, the need to provide sufficient excess water to suspend the soil removed in an aqueous liquor and, finally, the necessity to rinse the fabric.
Heating of the wash water is then the principal use of energy, and a minimum level of detergent becomes necessary in order for an effective concentration to be reached at the operating wash temperature. Means to improve mechanical action without increasing the water level used would, therefore, make any aqueous wash process significantly more efficient (i.e. yield further reductions in energy, water and detergent consumption). It should be noted that mechanical action itself has a direct effect on the detergent level, since the greater the level of soil removal which is achieved through physical force, the less that is required of the detergent chemistry. However, increasing the mechanical action in a purely aqueous washing process has certain associated drawbacks. Fabric creasing readily occurs in such processes, and this acts to concentrate the stresses from mechanical action at each crease, resulting in localised fabric damage. Prevention of such fabric damage (i.e. fabric care) is of primary concern to the domestic consumer and the industrial user.
In the light of these challenges which are associated with aqueous washing processes, the present inventors have previously devised a new approach to the problem, which allows the deficiencies demonstrated by the methods of the prior art to be overcome. The method which is provided eliminates the requirement for the use of large volumes of water, but is still capable of providing an efficient means of cleaning and stain removal, whilst also yielding economic and environmental benefits.
Thus, in WO-A-2007/128962, there is disclosed a method and formulation for cleaning a soiled substrate, the method comprising the treatment of the moistened substrate with a formulation comprising a multiplicity of polymeric particles, wherein the formulation is free of organic solvents. Preferably, the substrate is wetted so as to achieve a substrate to water ratio of between 1:0.1 to 1:5 w/w, and optionally, the formulation additionally comprises at least one cleaning material, which typically comprises a surfactant, which most preferably has detergent properties. In preferred embodiments, the substrate comprises a textile fibre and the polymeric particles comprise, for example, particles of polyamides, polyesters, polyalkenes, polyurethanes or their copolymers but, most preferably, are in the form of nylon beads.
The use of this polymeric cleaning method, however, presents a requirement for the cleaning particles to be efficiently separated from the cleaned substrate at the conclusion of the cleaning operation, and this issue is addressed in WO-A-2010/094959, which provides a novel design of cleaning apparatus requiring the use of two internal drums capable of independent rotation, and which finds application in both industrial and domestic cleaning processes.
In co-pending WO-A-2011/064581, there is provided a further apparatus which facilitates efficient separation of polymeric cleaning particles from the cleaned substrate at the conclusion of the cleaning operation, and which comprises a perforated drum and a removable outer drum skin which is adapted to prevent the ingress or egress of fluids and solid particulate matter from the interior of the drum, the cleaning method requiring attachment of the outer skin to the drum during a wash cycle, after which the skin is removed prior to operating a separation cycle to remove the cleaning particles, following which the cleaned substrate is removed from the drum.
In a further development of the apparatus of WO-A-2011/064581, there is disclosed in co-pending WO-A-2011/098815 a process and apparatus which provides for continuous circulation of the polymeric cleaning particles during the cleaning process, and thereby dispenses with the requirement for the provision of an outer skin.
Further benefits in terms of reduced power and consumable requirements for the cleaning method originally proposed in WO-A-2007/128962 have been disclosed in co-pending GB Patent Application No. 1018318.4, where the technology has been refined to achieve at least equivalent cleaning performance whilst employing significantly reduced levels of detergents and much lower process temperatures.
The apparatus and methods disclosed in the foregoing prior art documents have been highly successful in providing an efficient means of polymeric cleaning and stain removal which also yields significant economic and environmental benefits. The move to much lower wash temperatures has been particularly beneficial in this regard. As a consequence of the achievement of such lower temperatures, however, the need to control hygiene in the washing machine has become significantly more important. Hotter wash temperatures (>60° C.) can provide some level of hygiene control via thermal disinfection, since heat is an efficient destroyer of mould and bacteria, and higher temperatures are increasingly beneficial. When these polymeric cleaning processes are run at lower temperatures (<40° C.), however, hygiene considerations are magnified compared to the equivalent aqueous process, due to the presence of the polymeric particles. Said particles provide a large additional surface area contained within the washing machine, on which mould and bacteria can grow. The growth here can be accelerated by the fact that the particles remain moist for a considerable time after each wash process has been run, and the overall levels of mould and bacteria reached can be further increased if the machine remains unused for extended periods of time.
The hygiene problem in the polymeric cleaning machine can, of course, be controlled by similar means to that used in conventional aqueous domestic or industrial washing, namely the use of higher wash temperatures as noted above, and/or chemical additives in the wash water used. Suitable additives include chlorine derived bleaches (e.g. sodium hypochlorite) or oxygen derived bleaches (e.g. hydrogen peroxide), but the use of these materials has drawbacks in that they can decolour some garment types, and generally promote fabric damage through chemical attack. The oxygen derived bleaches also become less effective at lower wash temperatures (<40° C.), even when used in combination with suitable activators, e.g tetraacetyl ethylene diamine. Other additives based on chloro compounds (e.g. liquid chlorophenols) can also be used, but with similar drawbacks. Possibly the most benign means of achieving antimicrobial performance in the wash water is via the addition of silver-containing materials (e.g. silver-containing zeolite materials). Such approaches are expensive to consider, however, as they are effectively applicable for single wash use only. Furthermore, as in all cases with chemical additives in the wash water, there are effluent treatment considerations to take into account.
In looking to further develop the method of the cleaning process from WO-A-2007/128962 and co-pending GB Patent Application No. 1018318.4, therefore, the present inventors have now sought to provide a process which allows the aforementioned hygiene deficiencies with polymeric cleaning to be overcome, particularly at low wash temperatures (<40° C.). Hence, in the presently claimed invention, the inventors, by means of the addition of an antimicrobial agent to the polymeric particles, seek to provide a process in which lower levels of mould and bacterial growth occur within the washing machine at all times. The introduction of the antimicrobial agent in this way overcomes the drawbacks which would be associated with single use addition into the wash water (i.e. fabric damage, expense and effluent treatment considerations), and the action of the antimicrobial agent is continuous over the lifetime of the polymeric particles, which are re-used many times in subsequent washes, as is common practice with this technology.